it with a newer or better one. It is also illegal to tamper with emission control devices. The anti-tampering law applies to individuals as well as to businesses. Individuals may be fined as much as $2,500 for each vehicle tampered with, and businesses are subject to fines of up to $25,000.
Generally, you are allowed to install an aftermarket converter for these three reasons only:
1. If the converter is missing from the vehicle when the car is brought in for exhaust system repair.
2. If an inspection has determined that the existing converter has been lead-poisoned, damaged, or otherwise needs replacement.
3. If the vehicle is more than 5 years old or has more than 50,000 miles (8 years/80,000 miles for 1995 and newer vehicles) and a legitimate need for replacement has been established and appropriately documented (such as a plugged converter or unrepairable exhaust leaks).
Manufacturers of new aftermarket converters are required to offer a 5-year/50,000-mile warranty on the converter shell and end pipes. New catalysts must also be guaranteed to meet the Environmental Protection Agency (EPA) emission performance standards for 25,000 miles when the vehicle is properly used and maintained.
The EPA requires that a new, legal replacement catalytic converter must be properly labeled. Required labels on the converters have a series of letters and numbers in the following format:
N/XX/YYYY/ZZZZ
Here’s what that label means:
N = a new converter
XX = manufacturer’s code issued by EPA
YYYY = a numerical designation of the vehicle application or part number
ZZZZ = numeric month and year of manufacture
Converters manufactured for sale in California may have the letters “CA” in the first position. Because California standards are more stringent than federal EPA standards, these converters meet EPA requirements and are usually known as “50-state” units. Catalysts that comply with federal laws but not California regulations are known as “49-State” units. If the new catalytic converter does not have this kind of label it may not be a legal replacement part for any U.S. application, placing you in violation of federal law.
As the name implies, a cat-back system replaces the factory exhaust from the last catalytic converter to the exhaust tips at the rear of the car. This section of the exhaust system is where the mufflers are found. Desirable features in this part of the power system are high exhaust gas velocity and free flow with as few bends as possible.
Most aftermarket exhausts keep the basic tube size close to stock for the model of car to maintain exhaust gas velocity. Because of chassis size and underbody differences, exhausts that fit the 325/328/M3 models do not generally fit the 318 or 323 models. However, cat-backs fit two-door or four-door E36 models alike.
When choosing an aftermarket exhaust, apart from tubing size you need to look for smooth bends and joints in the pipe and unrestricted mufflers. Generally speaking, the freer the flow, the louder the exhaust, so there’s a tradeoff you need to understand before you buy. If you plan to drive your car daily, excess noise can become annoying and may be illegal. If you are building a dedicated track car, noise is usually less of an issue (within the bounds of the track’s noise limits).
The Corsa (RSC Reflective Sound Cancellation) cat-back exhaust for the BMW 328i is a quality piece of equipment. The stainless steel construction, TIG welding, great exhaust note, and performance enhancement all make this modification worth doing.
Horsepower and Torque Gains from Cat-Back Systems
Exhaust manufacturers often claim gains of 5 to 15 hp and a similar torque improvement from a good cat-back exhaust. The actual gain depends on several factors beyond the product you choose:
• What model of E36 are you upgrading? An M3 probably sees more benefit than a 325i or 328i because of the increased amount of air already flowing through the system.
• Have you already upgraded the cold-air intake, intake manifold, exhaust header, and catalytic converter mid-pipe?
• Engine tuning is necessary to fully realize the benefits of a less-restrictive exhaust.
In general, you see the best results if the exhaust is the most restrictive part of the system before the upgrade, but most people perform the easy cat-back exhaust upgrade before they do the more difficult and expensive header and catalyst upgrades. The catalyst is usually the restriction point, and as noted above, for legal reasons a catalyst delete pipe may not be an option.
The market offers many quality cat-back exhausts, and the main thing you care about is the way they sound. Some products have a drone at certain RPM levels, and some are quieter than others. Much of that difference depends on what’s been done to the engine already, because all aftermarket systems were designed and tested using otherwise stock cars. As with other parts, you’re going to get what you pay for, so beware of false economy. Akrapovic, Dinan, Magnaflow, Corsa, and Supersprint are generally well known for excellent results and they fit like original equipment. Off-brands tend to have fitment issues and use thinner metal and lower quality mufflers.
All aftermarket exhausts fall into the same general envelope of performance enhancement; there’s only so much power you can get out of a cat-back. If you go with a well-known and respected brand, you have a good unit that installs easily with the stock hangers. Custom exhaust systems with weld-in mufflers, such as Flowmaster, generally require more work to install, and you won’t really get any additional power benefits.
Project: Upgrading a Cat-Back Exhaust
The heart of the Corsa exhaust is the RSC mufflers, and the great-looking exhaust tips. The reflective sound cancellation system is designed to prevent exhaust drone by shaping the interior of the muffler to reflect and cancel sound that would otherwise build into a standing wave. One other reason to spend the money on a reputable, quality cat-back is the fit: A cheap unit may not have the proper clearances and can melt the bumper cover.
This project installs the Corsa RSC (Reflective Sound Cancellation) cat-back exhaust system on the project 1996 328i. This product uses twin 2.25-inch OD T-304 stainless tubes and dual mufflers. Inside the mufflers, the exhaust gases pass straight through; the mufflers are designed to reduce noise without impeding gas flow. With the previously installed cold-air intake, this is an obvious next step in performance modification.
Tip: If you’re considering installing a limited-slip differential or reinforcing the rear subframe mounts, now is a great time to do that, as you have to remove the exhaust from the car to do those projects.
If you have access to a safe automotive lift, this project is easy and convenient. You can do the work using only jack stands, but it takes longer and is more difficult. Always follow the manufacturer’s specific instructions.
Follow These Steps
